Wearable Patch and E-Skin From NC State Deliver Haptic Warnings for Environmental Hazards

Picture receiving an alert about poisonous gas or polluted water not as a phone notification you might overlook, but as a vibration you feel straight on your skin.

A research team has now created just that: a wearable patch that identifies environmental hazards-such as dangerous gases or heavy metals in water-and instantly notifies the wearer via vibration.

Using the same core approach, the researchers also reworked the platform into an “e-skin” that enables robots to sense hazards and steer clear of them without human input.

Faster warnings when seconds matter

The project was headed by Erim Uzunoğlu, a PhD student at North Carolina State University (NC State).

Although today’s sensors can already pick up environmental hazards and send alerts to a smartphone, the team set out to make the warning faster and harder to miss.

They focused on two key aims. The first was to miniaturise the sensing hardware and combine it into a wearable patch capable of flagging potential hazards.

“If you’re coming into contact with a hazardous substance, you need to know as quickly as possible,” said Uzunoğlu.

Since a phone alert may not be checked immediately, the researchers embedded haptic technology into the patch so it vibrates as soon as it detects a hazard-helping the wearer react sooner.

Breakthrough technology in a tiny wearable patch

The researchers produced a square patch that is slightly smaller than a driver’s licence, but still manages to hold a substantial amount of technology.

Within the patch sits a microcontroller that serves as the device’s brain, alongside a small battery and sensors capable of tracking six separate environmental hazards. A miniature actuator functions as the haptic motor, pulsing against the skin when a hazard is detected.

On the outside, the device features an array of thin-film photovoltaic cells. This allows it to continually harvest solar energy while being worn, helping to extend its limited battery life.

Designing a buzz you can’t miss

Including a vibrating motor alone was not sufficient-the sensation also had to be felt clearly and interpreted as meaningful.

“Just having a buzzing motor isn’t enough; you need to actually feel it,” said co-author Oluwatobi Ojuade, a PhD student at NC State. “We designed tiny textured surfaces that sit at the interface between the motor and your skin, almost like a miniature pattern of bumps.”

“By changing the size and spacing of those bumps, we could control how the vibration is perceived against your skin. That let us fine-tune the sensation so it grabs your attention instead of feeling like a faint buzz you might miss.”

Beyond that, the patch is designed to initiate a unique vibration pattern-or “haptic sequence”-for each hazard it recognises.

So wearers are not only alerted that something is wrong; they can also tell which environmental hazard is present from the way the patch vibrates on their skin.

Solar power keeps it running

Early results suggest the approach is working well.

“In proof-of-concept testing, we found that the device did a good job of detecting hazardous substances and immediately triggering the haptic response,” Uzunoğlu said.

“We also found the energy-harvesting technology did a good job of extending the battery life. Coupled with the sensors’ low power demands, this allows the device to function for around 24 hours.”

Reaching a full day of use is a notable step for a device of this size, as it means the patch can realistically operate as an all-day wearable rather than needing frequent recharging or replacement.

From human to robot skin

As the wearable patch came together, the team began exploring whether the same idea could be applied to robots-giving machines a way to detect environmental hazards and respond automatically.

That line of thinking resulted in what the researchers refer to as e-skin.

The e-skin is created by placing the sensor patch on top of a piezoelectric layer. When a sensor identifies a hazard, it activates the haptic response.

As the patch vibrates against the piezoelectric material, an electrical signal is produced, which the robot can sense and decode.

In proof-of-concept testing, this e-skin enabled quadrupedal robots to detect hazards and adjust their routes to avoid them.

These tests suggest that a sensing approach designed for human safety can be extended naturally to autonomous hazard avoidance in robotics.

Off-the-shelf parts

To build both the patch and the e-skin, the researchers relied largely on off-the-shelf components rather than specially engineered parts.

“The patch and e-skin are largely made using off-the-shelf components, with very few custom-engineered elements,” said co-corresponding author Amay Bandodkar, an assistant professor of electrical and computer engineering at NC State.

“That should make it easier to scale up the technology moving forward. The concept is extremely flexible – the sensor array is modular, so you can add or remove sensors that monitor for whichever hazards are most relevant.”

In principle, the same patch format could be repurposed for a wide range of applications.

By altering which hazards the wearable patch monitors, it could be used for workplace safety, environmental monitoring, or disaster response.

A breakthrough years in making

For Lilian Hsiao, co-corresponding author and an associate professor of chemical and biomolecular engineering at NC State, the work marks the resolution of a long-running technical obstacle.

“It’s quite amazing to see that we can encode tactile signals into materials with different properties,” she said. “It’s something that has been very challenging to do in the past, especially in real-world situations where people would want to wear the device.”

“Combining something people would wear with sophisticated sensing capabilities and the ability to alert the user is something we’ve been working toward for a long time.”